Alpha titanium alloys



United States atent fiice 2,777,768 Patented Jan. 15, 1957 2,777,768ALPHA TITANIUM ALLOYS No Drawing. Application August 3, 1953, Serial No.372,161

7 Claims. (Cl. 75-1755) The invention relates to titanium base alloyscontaining only the alpha phase below 825 C. and more particularly toquaternary alloys of titanium, aluminum, vanadium and silicon.

Titanium metal transforms from a body-centered cubic or beta crystalstructure or phase to a hexagonal closepacked or alpha crystal structureor phase on cooling from above 882 C. to below that temperature. Analloying element may be added to titanium to stabilize either the alphaor the beta structure. The effect of such an alloying element depends onwhether the atomic diameter of the alloying element best fits into thehexagonal close-packed structure or the body-centered cubic latticestructure.

The effect of such an alloying element may be to either raise or lowerthe transformation temperature and there are known alpha stabilizers andbeta stabilizers.

Alloying elements also may be added to titanium to develop someparticular desired property or properties addition of such alloyingelements may affect the alpha or beta crystal structure of titanium indifferent ways.

For instance, there are may alloying elements that can be added totitanium as strengtheners but many of such elements cause a lowering ofthe transformation temperature which may be undesirable. addition of oneor more alloying elements or metals to titanium for one purpose mayadversely afiect certain properties or characteristics that are desiredto be present or developed in the alloy or in products formed therefrom.

Aluminum, oxygen and nitrogen stabilize the alpha structure, andincreasing amounts of these elements raise the transformationtemperature. Below 825 C. aluminum is soluble in alpha titanium up to24% by weight before the formation of a second phase (probably TiAl)begins. Similarly nitrogen and oxygen have solubilities of 5% and 14%,respectively, in alpha titanium below 825 C. With these three elements,the amount which can be employed in titanium alloys, while stillmaintaining an all alpha structure below 825 C., is far greater than theamount which would be desired in titanium base alloys from otherconsiderations.

Columbium and vanadium, among others, are beta stabilizers, that is,their atomic size is such that they fit more satisfactorily into thebody-centered cubic lattice structure, thereby lowering thetransformation temperature with increasing additions. However, there isa restricted alpha field with these alloying elements which makespossible the addition of very small amounts of these elements whilepreserving an all alpha structure below 825 C. Columbium and vanadiumhave solubilities with alpha titanium at 825 C. of approximately 1% and1.5%, respectively.

When carbon, silicon or tungsten are added to titanium, there is arestricted alpha field; but instead of an alphabeta field to the rightof the all alpha region in .the equilibrium diagram, there is an alphaplus compound region.

In other words, the

' ed in a structure intended to be In the case of carbon, this compoundis titanium carbide. Although only 0.3% carbon is soluble in alphatitanium at 825 C. (the solubility decreases to 0.2% at 600 C.),additions of greater than 0.3% carbon do not change the basic alphastructure but merely cause the presence of titanium carbide particles inthe alpha matrix. Carbon can be intentionally added to'titanium alloys,if desired, and it imparts useful physical properties up to increasingthe tensile strength with a corresponding drop in ductility. Beyond thiscarbon content, ductility drops oif rapidly.

' Silicon is soluble in alpha titanium to an extent of 0.5% at 825 C.and any amount in excess of this forms the compound Ti5Si3, in the alphamatrix. High ductility titanium alloys have been made containing as muchas 1.5% silicon, and having a considerable amount of intermetalliccompound in the alpha matrix.

Tungsten does not form a compound as do carbon and silicon, and atungsten content of greater than 0.4% at 825 C. results in a mixedalpha-beta structure. Below 725 C., the alpha-beta region changes to analpha plus tungsten region but, because of the alpha-beta region presentfrom 725 C. to the transformation temperature of 882 C., no more than0.4% tungsten could be toleratcompletely alpha.

These considerations present a from such titanium alloy sheets. suchtitanium alloy sheets, the sheets must be rolled and the required hotrolling temperatures for producing such sheets are in the neighborhoodof 80 C. The rolling procedure may comprise hot rolling or may includeboth hot and cold rolling to gauge, followed by an annealing operationso that a ductile titanium alloy sheet is produced which may befabricated by forming or drawing to provide a desired part or endproduct.

Accordingly, it is a fundamental object of the present become brittle athigh temperatures. 7

Another object of the present invention is to provide titanium alloyswhich may be hot rolled into sheets of any desired gauge without harmfulembrittlement which may occur in hot rolling two phase titanium alloysheets. This embrittlement in alpha-beta type titanium alloys, in

This transformation product is such that the transformation cannot becontrolled during hot rolling and, because of this, the sheets cannot beannealed to form a consistently ductile material.

There can be no embrittlement caused by a transformation of themicrostructure during hot rolling, if no transformation occurs and notransformation products are formed during hot rolling. From thestandpoint of hot rolling titanium alloy sheets, it is desirable, if notnecessary, to heat the sheets being hot rolled 'to a rolling temperatureof above :800 C. Thus, if no transformation occurs on heating a titaniumalloy to or cooling it from 800 'C;, no embrittlement during hot rollingat such temperature can occur. 7

Accordingly, it is a further object of'the present invention to providea titanium alloy containing only the alpha phase below, say 825 0, thusraising the -trans formation temperature so that the crystal structureof the alloy does not change from alpha to beta and back from beta toalpha in heating the metal up to and rolling the metal at a rollingtemperature of 800 C., and permitting such alloy to be satisfactorilyhot rolled at 800 C.

More particularly, it is an object of the present invention to maintainan alpha structure in a titanium alloy which is stable at hot rollingtemperature, and during hot rolling and cooling, so as to eliminate theoccurrence of embrittlement during hot rolling such alloy into sheets ofdesired gauge.

It is a further object of the present invention to improve the weldingcharacteristics of titanium alloys. We

believe that for the same reasons discussed concerning embrittlementduring hot rolling, welds of low ductility result when weldingalpha-beta type titanium alloys even though high strength may be presentin such welds. Many alloying elements can be added to titanium tostrengthen the same, but unfortunately many of such elements lower thetransformation temperature and proand metastable beta phases, or thealpha and metastable beta-phases.

Moreover, it is an object of the present invention to provide an alphatitanium alloy containing no transformed or retained beta phase afterhaving been hot rolled to 0.040" sheet material at 800 C.

In Table 1 below, a comparison is shown between the physical propertiesof sheets of an alpha-beta titanium alloy containing 2.2% iron-2.7%vanadium-balance titanium, and an alpha titanium alloy containing 2%aluminum-0.5% vanadium-0.2%siliconbalance titanium. These propertieswere obtained in the following conditions: hot rolled, hot rolled andannealed, and cold rolled and annealed. Higher ductility is normallyexpected after cold rolling and annealing rather than after hot rollingand annealing. What is probably the most important diiference in the twoalloys, as regards their physical properties, is the hot rolled andannealed elongation values. The maintenance of high elongation in thealpha alloy is significant. Note the high elongation value of 18.4 inthe alpha alloy, as compared to the elongation value of only 7.8 in thealpha-beta alloy.

The ratios of hot rolled and annealed to cold rolled and annealedelongation values are 89% for the alpha alloy and 72% for the alpha-betaalloy. Elongation values as low as 4% in 2" have been obtained on 0.040thick hot rolled and annealed specimens from this particular alpha-betaalloy due to embrittlement during hot rolling.

TABLE I Comparison of the physical properties of a two phase and asingle phase titanium alloy Ultimate Tensile Strength, p. s. i YieldStrength at 0.2% Offset,

P Proportional Limit, p. s. i Percent Elongation in 2 Minimum BendValue:

Longitudinal Trauversen" Hardness, Rockwell A Modulus of Elasticity, p.s. i. 10

Alpha Beta. Alloy (2.2% Iron-- Alpha Alloy (2% Aluminum-$.50},Vanadiu1n0.2% Silicon-Bal- 2.7% Vanadium-Balance Tianco Titanium)tanium) Hot Hot Rolled Gold Rolled Hot Hot Rolled Cold Rolled Rolled 1Annealed 2 Annealed 9 Rolled 1 Annealed 2 Annealed 7.0 2. 5 2. 5 Brittle2. 1 2. 1

5. 0 2. 0 2. 5 Brittle 2. 1 2. l

1 The normal 'hot rolling procedure is as follows: hot roll thick platetransverse to the forging direction at 800 C. Reductions ofapproximately 0.050" per pass are taken to a thickness of 0.150 andreductions of approximately 25% per pass are taken thereafter. Thesesheets were hot rolled to 0.04

3 Annealing consists of heating in air at 700 O. for 1 hour and aircooling. I 3 These sheets were hot rolled to 0.100, sandblasted, coldrolled to 0.063, annealed, cold rolled to 0.040

and annealed.

vide low ductility. We have discovered that by raising thetransformation temperature and by narrowing the alpha-beta field-that isthe temperature range through which both alpha and beta can exist-to beas small as possible, there is an absence of any acicular transformationproduct in the alpha titanium alloy, providing ductile and high strengthWelds.

Moreover, it is an object of the present invention to provide an alphatitanium alloy having improved high I temperature physical propertiesover titanium alloys containing metastable beta or mixed alpha and beta,which may lose strength rapidly and become brittle at temperatures above400 C. In accordance with the present invention, the alpha titaniumalloys comprehended are stable up to 825 C. in the annealed condition.

Furthermore, it is an object of the present invention to provide analpha titanium alloy characterized by the absence of beta or thetransformed beta phase below 825 C. which results in the elimination ofbrittleness obtained in hot rolled annealed titanium alloy sheetscontaining both the alpha and'beta phases and the alpha Accordingly, itis a further object of the present invention toprovide an alpha titaniumalloy in which the hot rolled and annealed elongation values of sheets,such as 0.040 thick sheets, are exceedingly high due to the absence ofembrittlement during hot rolling.

A picture of the microstructure of the two phase titanium alloy setforth in Table 1, hot rolled to 0.040" sheet at 800 C. and annealed at700 C. for one hour with air cooling, shows a definitely two phasestructure, with very small particles, and no large grains evident. Thereis a medium amount of. small to medium size carbides, and the structureis typical-of one in which a brittle transformation product occurs onhot rolling.

In comparison, a picture of the microstructure of the alpha titaniumalloy set forth in Table I, after hot rolling to 0.040" at 800 C.,annealing at 700 C. for one hour and air cooling, shows a structurewhich is single phase with a few medium size carbides. Such picturesshow clearly that no harmful embrittlement has taken place in thissingle phase structure during hot rolling at 800 C.

2,772,708 ;I1lustra tive compositions and properties of alpha titave'lopcertain properties .or characteristics if carbon, nium alloys'embodyingthe invention appear in Table II oxygen and nitrogen are completelyabsent or only pres ent in very small quantities.- For instance, where aso= as follows:

TABLE II Minimum Bend Value Percent Con- Ult. en- N (lition sile Stu,

p. s. i.

Percent Percent Percent Percent I 1 v o 10.7 68.8 2 3.0 72.0 1 .4 07.0 2i 3 0 2 l 0.5 0.2 17.7 05.7 2 0.5 0.2 17.7 07.0 2 0.5 0.2 12.9 05.7 2 I0.5 0.2 11.; 00.4 14. 00.0 1 11.5 09.0

In Table II, the designation HR means hot rolled to called strongtitanium sponge is used, that is a raw -040 at 800 C. and thedesignation HRA means hot material which has higher than average oxygenand nitrorolled and annealed at 700 C. for one hour and air gencontents, an alloy containing 2% aluminum1% cooled after hot rolling.The percentages of alloying vanadium0.2% siliconbalance titanium is verysatiselements indicated in Table 11 are intended composition, factory.wet chemical analyses of bro 'en specimens sometimes It has been foundthat carbon, say from 0.050% to being at variance with the intendedcomposition. 0.6%, with or Without 0.010% to 0.1% nitrogen orIllustrative compositions and properties of alpha ti- 0.050% to 0.5%oxygen, or both oxygen and nitrogen, tanium alloys embodying theinvention and including may be used. Alpha titanium alloys of theinvention zirconium as an alloying element appear in Table III mayinclude either the minimum amounts of such elewhich also includesproperties of unalloyed titanium ments made with high purity titanium,or selected which does not have the improved properties of the alphaamounts thereof added to high purity titanium, or titanium alloys of thepresent invention, as follows: amounts thereof within the ranges statedwhen the alloy TABLE III Properties of. alpha titanium alloy sheets madefrom titanium base with zirconium as an alloying element in percentagesindicated l 1 Yield $00. Minimum Bend Percent Percent Percent Percent]Percent. Percent U10. Tenat 0.2% Pro. Percent Hard. Value 1 y Zr Si l Cl N Condition sile Stu, Offset, Limit, Elong. Rockp.'s. i. p. s. i. p.s. i. in 2" well A I L. T. I I g 2 l 2 0. 5 29 0115 HRA 125, 400 123,400 116, 200 14. 4 69 0 3 6 5 2 2 2 0. 2 2, 5 l 1 2 36 0196 ERA 103, 90098, 700 85, 350 15. 0 67 0 3. 6 2 1 3 1. 5 1 40 0155 ERA 110, 800 102,700 92, 400 14. 5 64 3 2.1 2 1 Unalloyed Titanium 61 0123 HRA 105, 80096, 900 84, 400 13. 5 64. 2 3. 6 2 1 Unalloyed Titanium 38 0098 HRA 74,150 62, 100 50, 200 23. 8 59. 9 0. 5 O 5 Unalloyed Titanium 53 0273 HRA83, 600 74, 100 66, 100 18. 7 58. 5 2. 1 1 0 The titanium base metalused in making the alpha titanium alloys of the present invention may behigh purity titanium metal or commercial titanium as normally produced.In either event, the titanium base metal may contain substances orimpurities normally found in either high purity titanium or commerciallypure titanium such as carbon, oxygen and nitrogen in amounts varyingwith the degree of purity.

Sometimes one or more of the elements, carbon, oxygen or nitrogen, mayintentionally be introduced in the alpha p titanium alloys of thepresent invention. For example, 10 elements, can be included in onetitanium alloy which all of the alpha stabilizers are potentstrengtheners in will still be all alpha. This is important because theconnection with carbon, oxygen and nitrogen, but they strength level ofthe resulting alloy depends on the amount are not so potent when carbon,oxygen and nitrogen are of alloying agents added, and a wide range oftensile absent. Thus, as a general rule, a greater amount of strengthsmay be obtained, depending on the amount or ,one or more alloyingelements may be necessary to deamounts of alloying elements present. Forinstance, if

is made from commercial titanium containing varying amounts of suchsubstances or impurities.

In the examples given in Tables II and III, the alloys in each instance,unless otherwise shown, contain approximately 0.02% nitrogen, 0.2%oxygen and 0.3% to 0.6% carbon.

We have unexpectedly discovered a most interesting and significantcharacteristic regarding the alpha titanium found in combination in atitanium alloy.

1.5% v.ot' X element,..and.0.5% of Y element, and, 3%

Atypical annealing operation of 0.040" sheets rolled from alpha titaniumalloys of the present invention may be carried outinamuflietype-air-fur-nace at 700 C..for

one hour with air cooling. Annealing of alloysof the present inventionin semi finished or finished form, other than sheets of the statedthickness, may be carried out in the manner just described.

In the foregoing tables the bend characteristics are measured as theradius upon which the sheets can be bent without fracture to an angle of75 the radius being stated as a multiple of the specimen thickness.

Although preferred percentages and combination percentages of thevarious addition elements in the alpha titanium alloys of thepresentinvention are given in Table ll, aluminum may be present in amounts offrom 0.50%

to 5.0%;vanadium may be present in amounts of from 0.50% to 3.0%; andsilicon from 0.05% to 1.5%. The maximum for vanadium is 3.0% since up tosuch an amount with the other alloying elements, vanadium hasa good andnot a detrimental affect on the alloy as awhole. Silicon has a tendencyto hold the elongation at a certain level andto obtain increasedstrength; and the percentage of silicon can be on the high side it thepercentages of aluminum and vanadium are on the low side.

Zirconium has been indicated in several of the examples in Table III asan alloying element. along with aluminum .and silicon or vanadium. Up to3% zirconium produces a good butanot outstanding strength-ductilityrelation.

The alpha titanium alloys of the present invention incorporate incombination-a number of desirable and outstanding, characteristics andproperties heretofore not Thus sheets hot rolled from such alloys have agood combinationof strength and ductility, providing as an averagev a115,000 p. s. i. minimum yield strength, with approximately 15%elongation in 2" as hot rolled or as hot rolled and annealed; along witha 3T minimum bend in sheets from 0.015" to 0.125; and provideweldability and lack of embrittlement at elevated temperatures up to 650C. for --four hours.

In addition to the foregoing, the alloys possess a workable degree ofreproduc'bility so as to be suitable for production if'properspecification requirements of the spongeraw material are met.

Another matter wort-hyof comment is the fact that aluminum andsiliconare good addition elements from the standpoint of lightness sincethey do not tend to increase the density of the resulting alloy.

aluminum, 0.50% ..to 3% hot rolled to 0.0 -.700 C- for onehourand aircooled, a115,000 p. s. i. v.minimum yield strength and about 15%elongation in2".

.Q ysen ans ai tn enh r bee in spia ld wss a .ills sl hIi 'sh' smallamounts as impurities in'titaniurn alloys; I to stabilize the hexagonalalpha structure and may be intentionally added for improvement ofphysical properties.

lficcordinglu the present invention provides new alpha titanium alloyshaving outstanding new characteristics and avoiding :d fliculties,defects and undesirable characteristics heretoi o'r eipresent inunalloyed titanium sheets or titanium alloy sheets, the examples givenbeing typical of the alloys andtheirproperties comprehended by thepresent invention.

We claim:

1. Analphatitanium .alloy composed of. in excess of 90% titanium, 0.50%to 5% aluminum, and the balance of said alloy being substantially onlyvanadium and silicon.

An alpha titanium alloy comprising 50% to 5.0% aluminum, .50% to 3%.vanadium, 05% to 1.5% silicon and the balance being substantially onlytitanium.

3. An alpha titanium alloy consistingessentially of 2 aluminum, 0.5%vanadium, 0.2% silicon and the balance substantially v only titanium.

,4. .An alpha titanium alloy consisting essentially of 2% aluminum, 1%vanadium, 0.2% silicon and the balance substantially only titanium.

5. An alpha titanium alloy comprising 0.50% to 5% aluminum, 0.50%vto.3%.vanadium,0.05% to 1.5% silicon and the balance titanium withcarbon, nitrogen and oxygen. as incidental impurities.

. 6..An alpha titaniumalloy comprising 0.50% to 5% vanadium, 0.05%silicon and .the balance titanium with incidental impuritiesofnot over0.6% carbon," 0.1% nitrogenand 0.5%

v oxygen.

7. Analphatitanium alloy comprising 050% to5% aluminum, 0.50%Yto.3%'vanadium, 0.0 '5% to 1.5% silicon and the balance being substantiallyonly titanium, the alloy being characterized by-the absence of the betaorthe trans formedbetaphase below 825 C. and by the absence ofbrittleness present in hot rolled annealed-titaniumalloysheetscontainingboththe alpha and beta phases, and being furthercharacterized'by having, as sheet at 800 C. and annealed at ReferencesCited in the fileof this patent UNITED STA TES PATENTS 'Swazyet a1. Dec.1, 1953 OTHER REFERENCES Titanium Project, Navy Contract No. Noa (5) 51-006-c;- Report No. 9 Final Report. Released asPB ;107l50,-Sept, 12,1952, pages 44 and 45, are most pe rtinent.

to.1.5% I

1. AN ALPHA TITANIUM ALLOY COMPOSED OF IN EXCESS OF 90% TITANIUM. 0.50%TO 5% ALUMINUM, AND THE BALANCE OF SAID ALLOY BEING SUBSTANTIALLY ONLYVANADIUM AND SILICON.